Search

Cytokine-induced β-cell apoptosis is a major pathogenic mechanism in type 1 diabetes (T1D). Despite significant advances in understanding its underlying mechanisms, few drugs have been translated to protect β-cells in T1D. Epigenetic modulators such as bromodomain-containing BET (bromo- and extra-terminal) proteins are important regulators of immune responses. Pre-clinical studies have demonstrated a protective effect of BET inhibitors in an NOD (non-obese diabetes) mouse model of T1D. However, the effect of BET protein inhibition on β-cell function in response to cytokines is unknown. Here, we demonstrate that I-BET, a BET protein inhibitor, protected β-cells from cytokine-induced dysfunction and death. In vivo administration of I-BET to mice exposed to low-dose STZ (streptozotocin), a model of T1D, significantly reduced β-cell apoptosis, suggesting a cytoprotective function. Mechanistically, I-BET treatment inhibited cytokine-induced NF-kB signaling and enhanced FOXO1-mediated anti-oxidant response in β-cells. RNA-Seq analysis revealed that I-BET treatment also suppressed pathways involved in apoptosis while maintaining the expression of genes critical for β-cell function, such as Pdx1 and Ins1. Taken together, this study demonstrates that I-BET is effective in protecting β-cells from cytokine-induced dysfunction and apoptosis, and targeting BET proteins could have potential therapeutic value in preserving β-cell functional mass in T1D. [ABSTRACT FROM AUTHOR]

Background: COVID-19 pandemic has caused more than 6 million deaths worldwide. Co-morbid conditions such as Type 2 Diabetes (T2D) have increased mortality in COVID-19. With limited translatability of in vitro and small animal models to human disease, human organ-on-a-chip models are an attractive platform to model in vivo disease conditions and test potential therapeutics. Methods: T2D or non-diabetic patient-derived macrophages and human liver sinusoidal endothelial cells were seeded, along with normal hepatocytes and stellate cells in the liver-on-a-chip (LAMPS – liver acinus micro physiological system), perfused with media mimicking non-diabetic fasting or T2D (high levels of glucose, fatty acids, insulin, glucagon) states. The macrophages and endothelial cells were transduced to overexpress the SARS-CoV2-S (spike) protein with appropriate controls before their incorporation into LAMPS. Cytokine concentrations in the efflux served as a read-out of the effects of S-protein expression in the different experimental conditions (non-diabetic-LAMPS, T2D-LAMPS), including incubation with tocilizumab, an FDA-approved drug for severe COVID-19. Findings: S-protein expression in the non-diabetic LAMPS led to increased cytokines, but in the T2D-LAMPS, this was significantly amplified both in the number and magnitude of key pro-inflammatory cytokines (IL6, CCL3, IL1β, IL2, TNFα, etc.) involved in cytokine storm syndrome (CSS), mimicking severe COVID-19 infection in T2D patients. Compared to vehicle control, tocilizumab (IL6-receptor antagonist) decreased the pro-inflammatory cytokine secretion in T2D-COVID-19-LAMPS but not in non-diabetic-COVID-19-LAMPS. Interpretation: macrophages and endothelial cells play a synergistic role in the pathophysiology of the hyper-inflammatory response seen with COVID-19 and T2D. The effect of Tocilizumab was consistent with large clinical trials that demonstrated Tocilizumab's efficacy only in critically ill patients with severe disease, providing confirmatory evidence that the T2D-COVID-19-LAMPS is a robust platform to model human in vivo pathophysiology of COVID-19 in T2D and for screening potential therapeutics. [ABSTRACT FROM AUTHOR]

Mitochondrial dysfunction occurs in most forms of heart failure. We have previously reported that Tead1, the transcriptional effector of Hippo pathway, is critical for maintaining adult cardiomyocyte function, and its deletion in adult heart results in lethal acute dilated cardiomyopathy. Growing lines of evidence indicate that Hippo pathway plays a role in regulating mitochondrial function, although its role in cardiomyocytes is unknown. Here, we show that Tead1 plays a critical role in regulating mitochondrial OXPHOS in cardiomyocytes. Assessment of mitochondrial bioenergetics in isolated mitochondria from adult hearts showed that loss of Tead1 led to a significant decrease in respiratory rates, with both palmitoylcarnitine and pyruvate/malate substrates, and was associated with reduced electron transport chain complex I activity and expression. Transcriptomic analysis from Tead1-knockout myocardium revealed genes encoding oxidative phosphorylation, TCA cycle, and fatty acid oxidation proteins as the top differentially enriched gene sets. Ex vivo loss of function of Tead1 in primary cardiomyocytes also showed diminished aerobic respiration and maximal mitochondrial oxygen consumption capacity, demonstrating that Tead1 regulation of OXPHOS in cardiomyocytes is cell autonomous. Taken together, our data demonstrate that Tead1 is a crucial transcriptional node that is a cell-autonomous regulator, a large network of mitochondrial function and biogenesis related genes essential for maintaining mitochondrial function and adult cardiomyocyte homeostasis. NEW & NOTEWORTHY Mitochondrial dysfunction constitutes an important aspect of heart failure etiopathogenesis and progression. However, the molecular mechanisms are still largely unknown. Growing lines of evidence indicate that Hippo-Tead pathway plays a role in cellular bioenergetics. This study reveals the novel role of Tead1, the downstream transcriptional effector of Hippo pathway, as a novel regulator of mitochondrial oxidative phosphorylation and in vivo cardiomyocyte energy metabolism, thus providing a potential therapeutic target for modulating mitochondrial function and enhancing cytoprotection of cardiomyocytes. [ABSTRACT FROM AUTHOR]

The molecular clock is intimately linked to metabolic regulation, and brown adipose tissue plays a key role in energy homeostasis. However, whether the cell-intrinsic clock machinery participates in brown adipocyte development is unknown. Here, we show that Bmal1 (also known as ARNTL), the essential clock transcription activator, inhibits brown adipogenesis to adversely affect brown fat formation and thermogenic capacity. Global ablation of Bmall in mice increases brown fat mass and cold tolerance, and adipocyte-selective inactivation of Bmall recapitulates these effects and demonstrates its cell-autonomous role in brown adipocyte formation. Further loss-and gain-of-function studies in mesenchymal precursors and committed brown progenitors reveal that Bmall inhibits brown adipocyte lineage commitment and terminal differentiation. Mechanistically, Bmall inhibits brown adipogenesis through direct transcriptional control of key components of the TGF-b pathway together with reciprocally altered BMP signaling; activation of TGF-b or blockade of BMP pathways suppresses enhanced differentiation in Bmall-deficient brown adipocytes. Collectively, our study demonstrates a novel temporal regulatory mechanism in fine-tuning brown adipocyte lineage progression to affect brown fat formation and thermogenic regulation, which could be targeted therapeutically to combat obesity. [ABSTRACT FROM AUTHOR]

Circadian disruption has deleterious effects on metabolism. Global deletion of Bmall, a core clock gene, results in β-cell dysfunction and diabetes. However, it is unknown if this is due to loss of cell-autonomous function of Bmall in β cells. To address this, we generated mice with β-cell clock disruption by deleting Bmall in β cells (β-Bmal1-/-). β-Bmal1-/- mice develop diabetes due to loss of glucose-stimulated insulin secretion (GSIS). This loss of GSIS is due to the accumulation of reactive oxygen species (ROS) and consequent mitochondrial uncoupling, as it is fully rescued by scavenging of the ROS or by inhibition of uncoupling protein 2. The expression of the master antioxidant regulatory factor Nrf2 (nuclear factor erythroid 2-related factor 2) and its targets, Sesn2, Prdx3, Gclc, and Gclm, was decreased in β-Bmal1-/- islets, which may contribute to the observed increase in ROS accumulation. In addition, by chromatin immunoprecipitation experiments, we show that Nrf2 is a direct transcriptional target of Bmal1. Interestingly, simulation of shift work-induced circadian misalignment in mice recapitulates many of the defects seen in Bmal1-deficient islets. Thus, the cell-autonomous function of Bmal1 is required for normal β-cell function by mitigating oxidative stress and serves to preserve β-cell function in the face of circadian misalignment. [ABSTRACT FROM AUTHOR]

Circadian clocks in adipose tissue are known to regulate adipocyte biology. Although circadian dysregulation is associated with development of obesity, the underlying mechanism has not been established. Here we report that disruption of the clock gene, brain and muscle Arnt-like 1 (Bmall), in mice led to increased adipogenesis, adipocyte hypertrophy, and obesity, compared to wild-type (WT) mice. This is due to its cell-autonomous effect, as Bmall deficiency in embryonic fibroblasts, as well as stable shRNA knockdown (KD) in 3T3-L1 preadipocyte and C3H10T1/2 mesenchymal stem cells, promoted adipogenic differentiation. We demonstrate that attenuation of Bmall function resulted in down-regulation of genes in the canonical Wnt pathway, known to suppress adipogenesis. Promoters of these genes (Wnt10a, β-catenin, Di-shevelled2, TCF3) displayed Bmall occupancy, indicating direct circadian regulation by Bmall. As a result, Wnt signaling activity was attenuated by Bmall KD and augmented by its overexpression. Furthermore, stabilizing β-catenin through Wnt ligand or GSK-3β inhibition achieved partial restoration of blunted Wnt activity and suppression of increased adipogenesis induced by Bmall KD. Taken together, our study demonstrates that Bmall is a critical negative regulator of adipocyte development through transcriptional control of components of the canonical Wnt signaling cascade, and provides a mechanistic link between circadian disruption and obesity. [ABSTRACT FROM AUTHOR]

Mitochondrial dysfunction occurs in most forms of heart failure. We have previously reported that Tead1, the transcriptional effector of Hippo pathway, is critical for maintaining adult cardiomyocyte function, and its deletion in adult heart results in lethal acute dilated cardiomyopathy. Growing lines of evidence indicate that Hippo pathway plays a role in regulating mitochondrial function, although its role in cardiomyocytes is unknown. Here, we show that Tead1 plays a critical role in regulating mitochondrial OXPHOS in cardiomyocytes. Assessment of mitochondrial bioenergetics in isolated mitochondria from adult hearts showed that loss of Tead1 led to a significant decrease in respiratory rates, with both palmitoylcarnitine and pyruvate/malate substrates, and was associated with reduced electron transport chain complex I activity and expression. Transcriptomic analysis from Tead1-knockout myocardium revealed genes encoding oxidative phosphorylation, TCA cycle, and fatty acid oxidation proteins as the top differentially enriched gene sets. Ex vivo loss of function of Tead1 in primary cardiomyocytes also showed diminished aerobic respiration and maximal mitochondrial oxygen consumption capacity, demonstrating that Tead1 regulation of OXPHOS in cardiomyocytes is cell autonomous. Taken together, our data demonstrate that Tead1 is a crucial transcriptional node that is a cell-autonomous regulator, a large network of mitochondrial function and biogenesis related genes essential for maintaining mitochondrial function and adult cardiomyocyte homeostasis. NEW & NOTEWORTHY Mitochondrial dysfunction constitutes an important aspect of heart failure etiopathogenesis and progression. However, the molecular mechanisms are still largely unknown. Growing lines of evidence indicate that Hippo-Tead pathway plays a role in cellular bioenergetics. This study reveals the novel role of Tead1, the downstream transcriptional effector of Hippo pathway, as a novel regulator of mitochondrial oxidative phosphorylation and in vivo cardiomyocyte energy metabolism, thus providing a potential therapeutic target for modulating mitochondrial function and enhancing cytoprotection of cardiomyocytes.

The circadian clock is an essential time-keeping mechanism that entrains internal physiology to environmental cues. Despite the well-established link between the molecular clock and metabolic homeostasis, an intimate interplay between the clock machinery and the metabolically active brown adipose tissue (BAT) is only emerging. Recently, we came to appreciate that the formation and metabolic functions of BAT, a key organ for body temperature maintenance, are under an orchestrated circadian clock regulation. Two complementary studies from our group uncover that the cell-intrinsic clock machinery exerts concerted control of brown adipogenesis with consequent impacts on adaptive thermogenesis, which adds a previously unappreciated temporal dimension to the regulatory mechanisms governing BAT development and function. The essential clock transcriptional activator, Bmal1, suppresses adipocyte lineage commitment and differentiation, whereas the clock repressor, Rev-erbα, promotes these processes. This newly discovered temporal mechanism in fine-tuning BAT thermogenic capacity may enable energy utilization and body temperature regulation in accordance with external timing signals during development and functional recruitment. Given the important role of BAT in whole-body metabolic homeostasis, pharmacological interventions targeting the BAT-modulatory activities of the clock circuit may offer new avenues for the prevention and treatment of metabolic disorders, particularly those associated with circadian dysregulation.

The molecular clock is intimately linked to metabolic regulation, and brown adipose tissue plays a key role in energy homeostasis. However, whether the cell-intrinsic clock machinery participates in brown adipocyte development is unknown. Here, we show that Bmal1 (also known as ARNTL), the essential clock transcription activator, inhibits brown adipogenesis to adversely affect brown fat formation and thermogenic capacity. Global ablation of Bmal1 in mice increases brown fat mass and cold tolerance, and adipocyte-selective inactivation of Bmal1 recapitulates these effects and demonstrates its cell-autonomous role in brown adipocyte formation. Further loss- and gain-of-function studies in mesenchymal precursors and committed brown progenitors reveal that Bmal1 inhibits brown adipocyte lineage commitment and terminal differentiation. Mechanistically, Bmal1 inhibits brown adipogenesis through direct transcriptional control of key components of the TGF-β pathway together with reciprocally altered BMP signaling; activation of TGF-β or blockade of BMP pathways suppresses enhanced differentiation in Bmal1-deficient brown adipocytes. Collectively, our study demonstrates a novel temporal regulatory mechanism in fine-tuning brown adipocyte lineage progression to affect brown fat formation and thermogenic regulation, which could be targeted therapeutically to combat obesity., (© 2015. Published by The Company of Biologists Ltd.)